Targeting next generation applications such as 400 Gigabit Ethernet (GE), high-baud rate and higher order modulation schemes, including 44 Gbaud dual polarization (DP)-64 Quadrature Amplitude Modulation (QAM) and 66 Gbaud DP-16QAM, involve precision calibration of optical and electrical components of an optical transceiver. Path timing, particularly between in-phase (I) and quadrature (Q) tributaries, are to be aligned with high accuracy, such as to a difference of 1 picosecond (psec). Frequency response characterization is also used to generate root-raise cosine frequency spectra for close packing of dense wavelength division multiplexed (DWDM) optical channels, and making optimum use of the effective number of bits of a digital-to-analog converter. Thus, proper and highly accurate frequency response characterization leads to correct compensation.
Pluggable optics provide advantages it terms of easy exchange of defective modules, sourcing from multiple vendors, and potentially reduced costs through volume manufacture. However, component tolerances and calibration inaccuracy become enhanced by the separation of optics and the application specific integrated circuit(s) since both linecards and pluggable modulates are to be calibrated separately.